Recording devices

ABSTRACT

A recording device comprising in series a first electrode, a layer containing a dispersed mixture of at least a semiconductor and an electrical insulator having one side contacting said electrode, a solid layer of an electrical insulator contacting the other side of the first mentioned layer, and a second electrode disposed on the other side of the solid insulator layer in electrical contact therewith. The second electrode may be either in direct abutting contact with the solid insulator layer or may act thereon through either a fluorescent phosphor layer or a photoconductive layer. When a voltage is applied between the electrodes, a charge of the same polarity as that of the first electrode is stored in both the layer of the mixture of semiconductor and insulator and in the solid insulator layer.

United States Patent Yamashita 1451 Mar. 28, 1972 [54} RECORDING DEVICES[56] llelerences clted [72] Inventor: Aklo Ylmashita, lkeda-shi, JapanUNITED STATES PATENTS M ts hi E] t i I d l C Ltd. 2,277,013 3/1942Carlson ..96/l.$ 73 Asslgnee 0 1; Japan c n p 2,739,243 3/1956 Sheldon.250/211 2,817,277 12/1957 Bogdonofi... .....96/1.5 Filed: Jan. 1 19692,853,383 9/1958 Keck ....96/l 2,896,507 7/1959 Mast et a1. ..96/1 X[211 APPL 793322 2,912,592 11/1959 Mayer ..25o/211 Rem! Application2,940,848 6/ 1960 Kostelec et a1.. 96/1 .8 X 3,057,719 10/1962 Byrne etal ..96/1 [63] Continuation of Ser. No. 350,830, Mar. 10, 1964,3,121,006 2/1964 Middleto 1 1, 96/1 5 abandoned. 3,124,456 3/1964 Moore..96/ 1.4 3,160,541 12/1964 Wollentin .1 17/218 X [30] ForeignApplication Priority Data 3,199,086 8/1965 Kallmahn et a1. ..96/ 1.5 X

21$, Egg: Primary Examiner charles E van Hem y 1963 Japan I I l I 38/2321 9 Attorney-Stevens, Davis, Miller & Mosher May 2, Japan i June 17,1963 Japan ..38/32395 1 June 21, 1963 Japan ..38/32532 A recordingdevice comprising in series a first electrode, a Sept. 21, 1963 Japan..38/50994 layer containing a i p r mixture of at least a semiconduc-Sept. 21, 1963 Japan ..38/50995 and an electrical insulator having oneside contacting Said Oct 25, 3 Japan 33 57 3 5 electrode, a solid layerof an electrical insulator contacting the Oct. 28, 1963 Japan ..38/58709other Side of the first mentioned layer, and a second electrode disposedon the other side of the solid insulator layer in elec- 521 U.S. c1..96/l.5,96/l.8 252/501 whim therewith The secmd elecimde may be either1 17/201 1 17/175 l17/2'l8 346/1 in direct abutting contact with thesolid insulator layer or may [51) CI 5 5/04 act thereon through either afluorescent phosphor layer or a [58]mid0152;313:1133:13311331113311:1311113155711415-1.8-phmnucnelayer-whenavongeisappndbetwemhe electrodes, a charge of the samepolarity as that of the first electrode is stored in both the layer ofthe mixture of semiconductor and insulator and in the solid insulatorlayer.

1 Claims, 20 Drawing Figures Fig. 5

PATENTEDW28 m2 3652, 270

SHEET 2 OF 6 Amount of charge (Am/frag Ufl/f) Inuenzor Vim a SHE 8 WWWATT0RNEY5 PATENTED MR 2 e 1972 Amounf of charge (Ara/fray un/f) Fig. 15

Amount of charge (Ara/frag um) SHEET 5 OF 6 77/778 (min) Fig. /7

Amomf of 0/70/99 (Arb/frary un/f) 0 i 2 3 4 T/me of vo/faga morass/0n(min) In uenz'or rQ/{io yamashia B/JMUZMMM/W ATTORNEYS RECORDING DEVICESThis application is a continuation of Ser. No. 350,830, filed Mar. 10,1964, and now abandoned.

The present invention relates to electrical devices and moreparticularly to a novel recording device of highly sensitive nature.

Sensitive paper for use in electrophotography has heretofore beenoffered as one type of recording device comprising a mixture of asemiconductor and an electrical insulator. The sensitive paper is soldby the commercial name of Electrofax, in which a mixture layer of zincoxide and a synthetic resin is coated on a sheet of paper. In thesensitive paper, however, an electrode formed of a plurality of finetungsten wires is spaced from the sensitive layer in order to charge thesensitive layer by the utilization of a corona discharge phenomenon.According to this method, a high discharge voltage of the order of 5,000to 6,000 volts is generally required and this is apparently undesirablein view of expensive power supply equipment and dangers involved in theoperation.

The invention provides a recording device with a structure which isentirely different from those of conventional devices, and the device ofthe invention acts in a manner that has not been known in the prior art.More precisely, the invention relates to a recording device whichcomprises a stack of a mixture of at least a semiconductor and anelectrical insulator, a carrier transformer, such as a conductor or asemiconductor, an electrical insulator, and an electrode. A mostremarkable feature of the invention resides in that an electric chargeof the same polarity with that of the carrier transformer in contactwith the mixture of the semiconductor and the insulator is stored in themixture.

The primary object of the invention is to provide a highly sensitiverecording device which comprises a mixture of at least a semiconductorand an electrical insulator, a carrier transformer brought into contactwith the mixture, another electrical insulator brought into contact withthe mixture on the opposite side of the carrier transformer, and anelectrode disposed on the another electrical insulator on the oppositeside of the mixture, to store in the mixture of the semiconductor andthe insulator a great amount of electric charge of the same polarity asthat of the carrier transformer in contact with the mixture.

Another object of the invention is to provide a recording device of saidcharacter in which the electrode is directly brought into contact withthe another insulator.

Still another object of the invention is to provide a recording deviceof said character in which the electrode is indirectly brought intocontact with the another insulator through another layer placedtherebetween.

Yet another object of the invention is to provide a recording device ofsaid character in which the semiconductor included in the mixture takesthe form of a P-type semiconductor, to store in the mixture at greateramount of electric charge of the same polarity as that of the carriertransformer in contact with the mixture.

Further another object of the invention is to provide a recording deviceof said character in which a fluorescent phosphor is added to themixture, to store in the mixture an electric charge of the same polarityas that of the carrier transformer in contact with the mixture and tovary the amount of electric charge by application of light thereto. 7

A further object of the invention is to provide a recording device ofsaid character in which a ferroelectric substance is added to themixture to store in the mixture a further greater amount of electriccharge of the same polarity as that of the carrier transformer incontact with the mixture.

A still further object of the invention is to provide a recording deviceof said character in which a fluorescent phosphor and a ferroelectricsubstance are added to the mixture, to store in the mixture an electriccharge of the same polarity as that of the carrier transformer incontact with the mixture and to vary the amount of electric charge byapplication of light thereto.

A yet further object of the invention is to provide a recording deviceof said character in which the mixture of the semiconductor and theinsulator further includes a metal generating a photo-electromotiveforce in combination with the semiconductor in the mixture, to store inthe mixture an electric charge of the same polarity as that of thecarrier transformer in contact with the mixture and to vary the amountof electric charge by application of light thereto.

Another object of the invention is to provide a recording device of saidcharacter in which the another electrical insulator takes the form ofsuch material as polystyrene or polyethylene having little residualelectric charge due to absorption current, to store in the mixture anelectric charge of the same polarity as that of the carrier transformerin contact with the mixture and to prevent the amount of electric chargefrom decreasing by an alternating electric field applied across themixture.

Still another object of the invention is to provide a recording deviceof said character in which a fluorescent layer including a fluorescentphosphor therein is superposed on the another insulator in contact withthe mixture, and the transparent conductive glass plate is superposed onthe fluorescent layer, to store in the mixture an electric charge of thesame polarity as that of the carrier transformer in contact with themixture and to vary the amount of electric charge by application oflight thereto.

Yet another object of the invention is to provide a recording device ofsaid character in which a photoconductive layer including therein aphotoconductor is superposed on the another insulator in contact withthe mixture and the transparent electrode is superposed on thephotoconductive layer, to store in the mixture an electric charge of thesame polarity as that of the carrier transformer in contact with themixture and to vary the amount of electric charge by application oflight thereto.

There are other objects and particularities of the invention which willbecome obvious from the following description with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic sectional view of a conventional recording device;

FIG. 2 is a schematic sectional view of a novel recording device of theinvention;

FIG. 3 is a graphic illustration of a relation between an amount ofelectric charge and applied DC voltage in the inventive and priorrecording devices;

FIG. 4 is a graphic illustration of a relation between a time of voltageapplication and an amount of electric charge in the inventive and priordevices;

FIG. 5 is a graphic illustration of a natural decay characteristic ofstored electric charges in the inventive and prior devices;

FIGS. 6-13 are graphic illustrations of various characteristics of theinventive device with the mixture of difierent compositions;

FIGS. 14-15 are graphic illustrations of the effect of insulators on thenatural decay characteristic of stored charges in the device of theinvention;

FIG. 16 is a schematic sectional view of another embodiment of theinvention;

FIGS. 17 and 18 are graphic illustrations of various characteristics ofthe device shown in FIG. 16;

FIG. 19 is a graphic illustration of the characteristic of the inventivedevice as applied to electrophotography; and

FIG. 20 is a schematic layout of the inventive device as applied toaudio and video recording.

The invention will now be described with reference to the drawings. WhenDC voltage is applied across a common electrical insulator placedbetween electrodes, electric charges produced on the respective faces ofthe insulator have opposite polarities to those of the electrodes withwhich it is in contact. Or more precisely, when DC voltage derived froma DC source 4 is applied across electrodes 2 and 3 having an electricalinsulator 1 interposed therebetween as shown in FIG. 1, a layer ofnegativecharges is formed at the boundary of the insulator 1 at which itcontacts the anode 2, while a layer of positive charges is formed at theboundary of the insulator 1 at which it contacts the cathode 3. In orderto produce a great amount of electric charge in the insulator 1, thereis a method which utilizes the persistent internal polarization effectof a fluorescent phosphor. According to this method, a mixture of anorganic insulating material and a fluorescent phosphor is used in lieuof the insulator 1 and DC voltage is applied to the mixture to causepolarization therein. The amount of polarization can be increased byillumination thereon and preserved for a long time in a dark space. Evenin this case, layers of electric charges of opposite polarities to thoseof the electrodes are formed at the boundaries of the insulator with theelectrodes as in the former case.

The device of the present invention is entirely different from suchconventional devices. According to the invention, an electric charge ofthe same polarity with that of a carrier transformer, such as aconductor or a semiconductor, is stored in a mixture of a semiconductorand an electrical insulator in contact with the carrier transformer. InFIG. 2, the device of the invention is schematically shown and comprisesa mixture 5 of an electrical insulator and a semiconductor and anelectrical insulator 6 placed between electrodes 7 and 8 which areconnected to a DC source 9. When, as shown in FIG. 2, DC voltage isapplied across the electrodes 7 and 8, an unipolar electric charge isstored in the mixture 5 and the insulator 6. Such effect was discoveredby the inventor and designated as a unipolar charge storage effect bythe inventor. The inventor considers that such effect is caused by theinjection of electric charges from the electrode 7 into the mixture 5.The inventor believes this to be the case because the electric chargestored in the mixture will have an opposite or negative polarity if anelectrical insulator is placed between the electrode 7 and the mixture5.

Hereinafter, the recording device with such feature of the inventionwill be explained in further detail. In the present invention, any ofwell-known semiconductors such as Ge, Si, Se, CU O, ZnO, PbO, NiO, CdS,ZnSe and anthracene may be used, and any of electrical insulators suchas glass, porcelain, silicone resin, polyvinyl chloride, polyvinylacetate, epoxy resin, polyvinyl butyral and wax may be used. There maybe many methods for manufacturing a material having the unipolar chargestorage effect by the use of these semiconductors and insulators. One ofthe methods includes mixing the semiconductor with the insulatingmaterial of organic nature such as the resin or wax, while anothermethod includes mixing the semiconductor with the insulating material ofinorganic nature such as glass, porcelain, or sulfur.

1. Basic characteristics Description will hereinunder be made withregard to basic characteristics of the recording device of theinvention. The effect of the invention will not vary by employing eithera conductor or a semiconductor as a carrier transformer. A mixtureincluding 70 percent of Cu O, a P-type semiconductor, and 30 percent ofsilicone resin is prepared and coated on a sheet of paper. The papercarrying the mixture thereon is placed between two electrodes in orderto obtain a structure as shown in FIG. 2. For the sake of comparison, amixture including 70 percent of (Zn, Cd)S, being a fluorescent phosphorshowing a persistent internal polarization effect, and 30 percent ofsilicone resin is prepared and placed between two electrodes in order toobtain a conventional structure as shown in FIG. 1. 1-1. Voltagecharacteristic FIG. 3 shows a relation between an amount of electriccharge and applied voltage when DC voltage is applied for 4 minutes tothe inventive and prior devices. In FIG. 3, the positive value shows anamount of positive charge and the negative value an amount of negativecharge. Curves l0 and 11 represent the characteristic of the priordevice wherein the curve 10 therein shows a variation in the amount ofcharge at the surface of the mixture layer at which it is in contactwith the anode, while the curve 11 shows a variation in the amount ofcharge at the surface of the mixture layer at which it is in contactwith the cathode. From the curves 10 and 11, it will be seen that thenegative charges are induced on the surface of the mixture layer whichis in contact with the anode and the positive charges are induced on thesurface in contact with the cathode. Curves 12 and 13 show the case ofthe invention, in which the curve 12 shows a variation in the amount ofcharge at the surface of the mixture layer which is in contact with theanode and the curve 13 shows a variation in the amount of charge at thesurface of the insulator layer which is in contact with the cathode.From the curves l2 and 13, it will be seen that the electric charge ofthe same polarity with that of the electrode with which the mixturelayer is in contact is stored in the mixture layer. This is the unipolarcharge storage effect which has not been found heretofore. The amount ofstored charges increase rectilinearly with relation to the appliedvoltage, and the effect of the invention appears already in a lowvoltage range. Therefore, it will be known that such effect is notproduced by some secondary cause such as local discharge but by thephenomenon of charge injection which has not been found in any of priordevices.

1-2. Voltage application time characteristic FIG. 4 shows a relationbetween a time of voltage application and an amount of electric chargewhen DC voltage of 600 volts is applied on the samples. A curve 14therein shows a case of the prior device and it will be'seen thatnegative charges are obtained on the side of the anode. In a curve 15showing the case of the present invention, positive charges are obtainedon the side of the anode. In both cases, the stored charges abruptlyincrease simultaneously with the application of voltage and saturationtakes place after about 4 minutes. These curves can be approximatelyexpressed as a formula P P w [1 exp (-M)], where P is an amount ofcharge after application of voltage for a long period, and A is aconstant which is compared with a reciprocal of a dielectric relaxationtime.

1-3. Natural decay characteristics FIG. 5 shows a variation in theamount of stored charge with relation to time when the inventive andprior devices are left to stand, or a natural decay characteristic.Curves 16 and 17 show variations in the amounts of negative and positivecharges when measurement is taken on the side of the anodes of the priorand inventive devices, respectively. It will be seen from the curvesthat the amount of stored charge decreases greatly in an initial periodof time and the decay becomes gradually less thereafter. These curvescan be approximated by a formula P= P 0 exp (t/'r), where P is aconstant and r is a time constant.

From the foregoing description with regard to the basic characteristicsof the device of the invention, it will be understood that, by thefeature of the invention, it is possible to store in a mixture of asemiconductor and an insulator an electric charge of the same polaritywith that of an electrode with which the mixture is in contact and toobtain a greater amount of charge than by the prior device. Therefore,the recording device of the invention is advantageous in that loss ofelectric charge is less when the electrode is spaced from the mixturedue to the fact that both have the same polarity and in that a goodsensitivity can be obtained owing to a great amount of electric chargestored therein.

2. Effect of different compositions of mixture Description will now bemade with regard to the effect of various semiconductors used in themixture and addition of fluorescent phosphors, ferroelectric substancesand metals thereto.

2-1. Effect of P-type semiconductor Cu O which is a P-type semiconductoris mixed with an organic electrical insulator in the form of siliconeresin. The mixture is coated on a Mylar film, being an electricalinsulator, to obtain a structure as shown in FIG. 2. After applicationof DC voltage of 600 volts for 1 minute, measurement is taken of theamount of charge at the surface of the mixture at the side of the anodeto obtain the natural decay characteristic,

and a curve 18 in FIG. 6 is obtained. In this case, positive charges arealso stored in the mixture of the anode side thereof. In case Se, one ofsimilar P-type semiconductor, is used, a curve 19 in FIG. 6 is obtainedunder the same condition. It will be apparent from the curve 19 that,though a great amount of electric charge is stored in the initial periodof time, its decay is quite rapid.

2-2. Effect of N-type semiconductor ZnO is used as a N-typesemiconductor and silicone resin is used as an electrical insulator. Inthis case, an electric charge of single polarity is also stored by theapplication of voltage as in the case of foregoing paragraph 2-l, but anamount of charge is less than about one half of the case of Cu O. Thestored electric charges can be preserved for a long time in a darkspace, but, in the case of ZnO, decrement of the charges is more rapidthan in the case of Cu O, as shown by a curve 20 in FIG. 6. The N-typesemiconductor has a remarkably smaller amount of stored charge than inthe P-type semiconductors and similar results have been obtained onother N-type semiconductors. Especially when CdS, another N-typesemiconductor, is used, almost no charge can be stored.

2-3. Effect of joint use of semiconductor and fluorescent phosphor AP-type semiconductor in the form of Cu,0, an organic insulator in theform of silicone resin and a fluorescent phosphor in the form of (Zn,Cd)S are mixed together with a solvent comprising toluene, coated on asheet of paper of insulating material, and sufficiently dried. A brassplate and a plate of transparent conductive glass havingthereon a tinoxide film are used as electrodes. The glass electrode is used for thepurpose of observing an effect of illumination on the mixture.

A sample without Cu 0 therein, that is, a sample in which powder of (Zn,Cd)S is solely dispersed in the silicone resin is prepared and DCvoltage of 600 volts is applied thereon in a dark space or withillumination thereon. Then, a layer of negative charge is formed on theanode side and a layer of positive charges is formed on the cathodeside. FIG. 7 shows a relation between an amount of charge thereby formedand a time of voltage application. Curves 21, 22, 23 and 24 in FIG.7'show a case wherein voltage is applied in a dark space and measurementis taken on the cathode side, a case wherein voltage is appliedsimultaneously with illumination with light of 50 luxes and measurementis taken on the cathode side, a case wherein voltage is applied in adark space and measurement is taken on the anode side, and a casewherein voltage is applied simultaneously with illumination with lightof 50 luxes and measurement is taken on the anode side, respectively.From the curves, it will be seen that layers of electric charges havingthe polarities opposite to those of the electrodes are formed in thesilicone resin wherein the fluorescent phosphor is dispersed.

Then, the semiconductor, Cu O, is mixed with the fluorescent phosphor,(Zn, Cd)S, at a ratio of l to and the mixture is dispersed in thesilicone resin to obtain a sample. By applying DC voltage of 600 voltsthereto in the above manner, an unipolar electric charge is stored inthe sample. FIG. 8 shows a relation between an amount of charge and atime of voltage application in this case. Solid lines 25 and 26 thereinshow a case wherein voltage is applied in a dark space and measurementis taken on the anode side, and a case wherein voltage is applied in adark space and measurement is taken on the cathode side, respectively.Dotted lines 27 and 28 show cases wherein voltage is applied whileilluminating with light of 50 luxes and measurement is taken on theanode and cathode sides, respectively. It will thus be seen that, by theaddition of the semiconductor for example Cu O, the mixture storestherein an electric charge of the same polarity with that of theelectrode with which it contacts and the amount of charge so stored isextremely great. Further, the amount of charge increases in proportionto the time of voltage application. The electric charge of singlepolarity thus formed can be storaged for an extended period of time,especially even in a light space. The charge may be extinguished by theapplication of an infrared light or by heating.

Then, a sample including 30 percent of an insulator or silicone resinand 70 percent of a mixture of a semiconductor for example Cu O and afluorescent phosphor or (Zn, Cd)S is prepared, and the mixing ratio of(Zn, Cd)S in the mixture is varied to obtain a relation between anamount of charge and the mixing ratio of (Zn, Cd)S, which is shown inFIG. 9. The amount of charge is measured on the anode side. It will beseen that positive charges are obtained by the mixture of thesemiconductor, Cu,O, of about 2 percent and the unipolar charges canthereby be stored. In the case of the mixture of shown in FIG. 2 andvoltage is applied thereto. As a result thereof, an electric charge ofthe same polarity with that of the electrode 7 is storaged in themixture 5. FIG. 10 shows a variation in the amount of stored charge whenthe mixing ratio of BaTiO to NiO is varied. It will be seen that theamount of charge increases at the BaTiO content of less than 60 percent,but abruptly decreases when the BaTiO content exceeds 60 percent. Thistendency is quite similar for any other ferroelectric substances. 2-5.Effect of joint use of semiconductor, fluorescent phosphor andferroelectric substance A semiconductor in the form of MD, a fluorescentphospher in the form of (Zn, Cd)S and a'ferroelectric substance in theform of BaTiO are mixed at a ratio of :10:10 and dispersed in siliconeresin to prepare a sample. FIG. 11 shows a relation between an amount ofcharge and applied voltage when voltage is applied on the sample in adark space. Measurement is likewise taken on the anode side, and it willbe seen that the charge of the same polarity with that of the electrodewith which the mixture contacts in storaged in the mixture. It will thusbe known that, by the addition of the fluorescent phosphor and theferroelectric substance, the amount of charge increases in a logarithmicmanner and great increase is effected especially in a high-voltageregion. 26. Effect of joint use of semiconductor and metal The effect ofthe invention can equally be obtained by a mixture of a semiconductorand a metal. Especially by employing a metal which may develop aphotovoltaic effect through contact with a semiconductor, it is possibleto vary an amount of charge stored in the mixture by varying the amountof light'applied thereto. Cu O is now selected as the semiconductorshowing the photovoltaic effect. Cu O, Cu and silicone resin are mixedat a ratio of 65 percent, 5 percent and 30 percent. In this case, bothof Cu O and Cu are mixed in a powdered state. The mixture is coated on aMylar film to provide a sample. The powder of Cu O and Cu may preferablyhave a similar grain size and may be as fine as possible, in the orderof 2 to 3 microns. This sample is incorporated in a structure as shownin FIG. 2 and voltage is applied thereon in a dark or a light space. Aplate of transparent conductive glass is selected as the electrode 7 inorder to see an effect of illumination. FIG. 12 shows a relation betweenan amount of charge (in an arbitrary unit) stored in the mixture layerand a time of application of voltage of 600 volts with the transparentelectrode 7 operating positive. Curves 29 and 30 therein show thecharacteristic in the dark space and the characteristic when illuminatedwith light of I00 luxes simultaneously with the application of voltage,respectively. From FIG. 12, it will be apparent that the amount ofstored charge was increased by the illumination, and in both cases, apositive charge is stored and has the same polarity with that of theelectrode with which the mixture layer is in contact. This is consideredthat the amount of charge is increased due to the photovoltaic effectproduced by the combination of Cu O and Cu when subjected to light. Itis further considered that this increased charge is not evolved from theinterior of the mixture layer by the photovoltaic effect, but byadditional charges drawn out of the electrode by an electric fieldproduced by the photovoltaic effect.

FIG. 13 shows a decrement of the stored charges when left to stand in adark and a light space. A curve 31 therein shows a variation in theamount of charge stored in the mixture when voltage of 600 volts isapplied on the sample for 1 minute in a dark space with the transparentelectrode operating positive and then the sample is left to stand in thedark space. A curve 32 shows a variation in the amount of charge storedin the mixture layer when voltage of 600 volts is likewise applied onthe sample for 1 minute in a dark space with the transparent electrodeoperating positive and then the sample is left to stand while beingilluminated with light of 100 luxes. From the curves, it will be seenthat the charge decreases less in the light space than in the darkspace. It is considered that this is because an electric field is formedby the photovoltaic effect between Cu O and Cu by the application oflight and any extinction of the charge is thereby prevented. Thesephenomena are also observed,.for example, in the combination of Se andCd, and Si of P-type and N-type, in addition to the abovedescribedcombination of Cu O and Cu.

3. Effect of residual electric charge in insulator In the recordingdevice of the invention, the insulator 6 as shown in FIG. 2 isabsolutely necessary. This insulator has a remarkable influence on theunipolar charge stored efiect, and a great amount of storaged charge canbe obtained by virtue of the presence of the insulator. Next descriptionwill be directed to the effect of such insulator.

A P-type semiconductor such as Cu O is mixed with silicone resin as inthe former cases, and the mixture is coated on various insulators toprovide samples having a structure as shown in FIG. 2. DC voltage and ACvoltage are applied across the samples in superposed relation. In FIGS.14 and 15, solid lines show a natural decay characteristic, or avariation in an amount of stored charge when the charge isfirst-storaged in the samples by the application of DC voltage of 200volts and AC voltage of 100 volts and subsequently the samples are leftto stand at no load, while dotted lines therein show a relation betweenan amount of stored charge and a time of AC voltage application when ACvoltage of 100 volts is solely applied. Curves 33 and 34, 35 and 36, and37 and 38 in FIG. 14 represent the cases of a Mylar film, paper and acyano'ethylcellulose, respectively, while curves 39 and 40, and 41 and42 in FIG. 15 represent the cases of polystyrene and polyethylene,respectively. Prominent results thereby obtained are that, although thecharge decreases by the application of AC voltage in the Mylar film,paper and cyanoethylcellulose in which exists a residual electric chargedue to absorption current, the charge would not decrease by theapplication of AC voltage in the polystyrene and polyethylene in whichthere exists almost no residual electric charge due to absorptioncurrent as shown in FIG. 15.

4. Effect of superposition of another layer on insulator layer In theforegoing, the description has been made with regard to the recordingdevice having the structure as shown in FIG. 2, but hereinunder,description will be made with regard to a structure wherein afluorescent layer or a layer including therein a fluorescent phosphor,or a photoconductor layer or a layer including therein a photoconductoris superposed on the insulator 6 of FIG. 2.

4-l. Superposition of fluorescent layer including therein fluorescentphosphor By superposing a fluorescent layer or a layer including thereina fluorescent phosphor on the insulator layer, an amount of electriccharge can be varied by application of light thereto. FIG. 16 shows astructure of such device, which comprises a plate 43 of transparentconductive glass, a layer 44 including a fluorescent phosphor having aninternal polarization effect, a layer 45 of an insulator, a layer 46 ofa mixture of a semiconductor and an insulator, and a metal electrode 47.

When, in this device, DC voltage is applied across the transparentconductive electrode 43 and the metal electrode 47, a layer of chargeshaving the same polarity with that of the elec' trode 47 is formed atthe face of the mixture layer 46 which contacts the metal electrode 47.When light is applied from the side of the transparent conductiveelectrode 43, the amount of charge in the fluorescent layer 44 variesand the amount of charge in the mixture layer 46 is thereby varied.

Now, suppose that the device of FIG. 16 comprises the fluorescent layer44 of a mixture of (Zn, Cd)S and silicone resin, the insulator layer 45of a Mylar film, and the mixture layer 46 of Cu O and silicone resin.FIG. 17 shows a relation between an amount of charge at the surface ofthe mixture layer 46 on the side of the metal electrode 47 and a time ofvoltage application when DC voltage of 500 volts is applied to thedevice while applying light of various illuminations. Curves 49, 50 and51 therein show a case of voltage application in a dark space, and casesof illumination with light of 20 and 40 luxes simultaneously withvoltage application, respectively. It will be seen that any of thecharges has the same polarity with that of the metal electrode 47 andthe amount of charge varies depending upon the illumination of light.4-2. Superposition of photoconductive layer including thereinphotoconductor In lieu of the fluorescent layer, a photoconductor layeror a layer including therein a photoconductor may be superposed on theinsulator layer to vary the amount of charge by application of light. Aphotoconductor layer is substituted for the fluorescent layer in thestructure of FIG. 16. The photoconductive layer comprises powder ofcadmium sulfide dispersed in silicone resin and is coated in a thicknessof about 60 microns on a plate of transparent conductive glass. Then afilm of polyethylene terephthalate of 12 microns thick is bonded on thephotoconductor layer, and a mixture layer comprising Cu O powerdispersed in silicone resin is coated thereon in a thickness of 60microns. A brass plate is used as an opposite electrode to obtain astructure as shown in FIG. 16. DC and AC voltages are applied insuperposed relation across the transparent conductive glass electrodeand the metal electrode. The AC voltage has a value of volts at 60cycles and the DC voltage is varied over various values with the metalelectrode operating positive. A curve 52 in FIG. 18 shows a relationbetween the DC voltage applied in a dark space and an amount of chargein the mixture layer. From the curve 52, it will be seen that, in a darkspace, the amount of charge of the same polarity with that of the metalelectrode increases with relation to an increase in the DC voltage.Curves 53 and 54 show a variation of an amount of charge when thevoltage is applied in the same manner under exposure with light of 20and 100 luxes, respectively. In each case, the amount of chargeincreases at first with the increase in the DC voltage, but suddenlydecreases at a certain voltage. The device with such structure issuitable for recording a signal in the form of light. 5. Application Inthe foregoing description, detailed explanation has been given withregard to the unipolar charge storage effect forming the basic principleof the invention and this principle can readily be applied to providevarious useful devices. 5-1. Electrophotography Electrophotography hasheretofore been carried out according to the following method. In theprior method, a high voltage of 5,000 to 6,000 volts is applied togenerate a corona discharge to thereby charge ZnO sensitive paper or Sesensitive plate uniformly all over its entire surface. By projecting animage on the charged ZnO sensitive paper or Se sensitive plate, chargeson portions hit by the light solely disappear due to photoconductivityof ZnO or Se. Therefore, charged portions and non-charged portionsarefor'medon the ZnO'sensitive paper 01' Se sensitive plate and a latentimage is produced by the distribution of the charges. Development can beeffected by applying thereto colored powder having charges opposite inpolarity to the charges on the sensitive paper or plate.

There has also been proposed an electrophotography, that is, P.l.P.applied electrophotography which utilizes the persistent internalpolarization effect of a fluorescent phosphor. According to such method,voltage of about 500 to 1,000 volts is applied on sensitive paper havingthereon a fluorescent phosphor to charge the sensitive paper by thepersistent internal polarization effect of the fluorescent phosphor. Byprojecting an image thereon, the charges on portions hit by the lightsolely disappear and a latent image of electric charges is formed on thesensitive paper. .A photograph is obtained by developing the image in amanner similar to the former method. In any of both methods, the latentimage on the surface of the sensitive paper is defined by chargedportions and non-charged portions. Such manner of charge distribution isdefective in that boundaries between the charged portions and thenon-charged portions are not so clearly defined. Due to such drawback,in the P.I.P. applied electrophotography, an electric field opposite tothe one used in the charging operation is simultaneously applied duringthe image projection to form the latent images on the surface of thesensitive paper by the charges of opposite polarities to each other tothereby improve the sharpness of the image. This method, however,involves a troublesome operation of changing over the electric field.

According to the invention, however, latent images with charges ofopposite polarities to each other can be formed on the surface ofsensitive paper by the utilization of the unipolar charge storage effectwithout any troublesome procedure of changing over the electric field.In the invention, a material adapted for the purpose comprises a mixtureof a semiconductor and a fluorescent phosphor dispersed in an insulatorand is incorporated in a structure as shown in FIG. 2. Fluorescentphosphors showing the persistent internal polarization effect arepreferred, which are (Zn, Cd)S, ZnS, CdS and the like.

FIG. 19 shows a relation between an amount of charge and a time ofvoltage application in various samples. Measurement of the amount ofcharge is taken at the anode side. A curve 55 in FIG. 19 represents acase of a sample including a mixture of a semiconductor and aninsulator. It will be seen that charges of the same polarity with thatof the electrode with which the mixture contacts are formed in themixture by the unipolar charge storage effect of the invention. Theamount of charge is almost free from the influence of light. A curve 56represents a case of a sample including a mixture of a fluorescentphosphor and an insulator, corresponding to the case of the prior P.I.P.applied electrophotography, and shows an amount of electric charge in adark space. A curve 57 shows a variation in an amount of charge in adark space in a sample including a fluorescent phosphor and asemiconductor dispersed in an insulator. It will be seen that thepolarity of charge is reversed after a certain time. This is because thecurve 57 is actually a resultant curve of the curves 55 and 56. A curve58 shows a variation in the amount of charge when light is projected onthe mixture of the fluorescent phosphor and the insulator simultaneouslywith the application of voltage, and it will be seen that the amount ofcharge increases with the application of light.

When light is projected on the mixture of the fluorescent phosphor,semiconductor and insulator, an increase in the amount of charge takesplace solely in the fluorescent phosphor component, and a curve therebyobtained takes the form of a combination of the curves 55 and 58, or aresultant curve 59 in which it will be seen that the polarity of chargeis reversed in a short time. When, therefore, the mixture of thefluorescent phosphor, semiconductor and insulator is used as a materialfor electrophotography, and an image is projected thereon underapplication of voltage, portions which are not hit by the light arecharged in a manner as shown by the curve 57. Then, when the applicationof voltage and image projection are ceased at a time corresponding topoint P, latent images of positive and negative charges are formed onthe surface of the sample on the anode side thereof. A positive and anegative image can be obtained by applying colored powder which ischarged negative and positive, respectively. According to the invention,an image of high sharpness can easily be obtained by virtue of thelatent images by the positive and negative charges, unlike the priorelectrophotography which relies on a corona discharge. Further, thewellknown PIP. applied electrophotography requires a troublesomeoperation of reversing the electric field, but according to theinvention, the application of voltage and image projection aresimultaneously made so that latent images of positive and negativecharges can be obtained at a time. The invention is further advantageousin that a working voltage less than 800 volts suffices.

5-2. Audio and video recording device.

A prior video recording method comprises applying an electrical signalcorresponding to pictures to a tape having thereon a ferromagneticmaterial to thereby record the signal in the form of a magnetic signal.According to the invention, however, video recording can be effected ina simple and inexpensive manner by the utilization of the unipolarcharge storage effect. A tape 61 carrying thereon a mixture 60 havingthe unipolar charge storage effect is made to pass between electrodes 62and 63 as shown in FIG. 20. The mixture 60 is composed of asemiconductor and an insulator, and the tape 61 is made of an insulatingmaterial such as a plastic, while the electrodes 62 and 63 are of brassof cylindrical shape. When voltage is applied across the electrodes 62and 63, positive or negative charges are formed in the mixture 60depending on the positive or negative polarity of the electrode 62. Theamount of charge so formed corresponds to the magnitude of the appliedvoltage. By applying the voltage signal in the form of a video signal,charges corresponding to the video signal are formed on the tape. Thecharged tape can be preserved for an extremely long time in a dark spaceand for a fairly long time in a light space too. The charges willhowever disappear by application of an intense infrared light.

The charges thus formed on the tape are then detected by a detector 64,taken out in the form of an alternating current corresponding topotentials on the tape, and reproduced as pictures. An advantageousfeature in this case is that the detector 64 need not abut the tape,which is therefore free from being injured. Further, the charges stillremain on the tape even after they have been taken out as the electricalsignal by the detector 64 and remain effective for repeated use. Thecharges carried on the tape can be erased by the application of anintense infrared light thereto and the tape is ready for subsequentvideo recording. According to the invention, it is possible to attainclose recording of even minute portions compared with the prior methodin which a magnetic material of considerable great size is used, and toobtain markedly high resolving power and fidelity which are of vitalimportance for a video recording device.

In accordance with the same principle, sound can likewise be recorded onthe tape. By applying a voltage corresponding to a sound current to thetape, charges corresponding to the sound can be formed on the tape. Thetape is then fed past the detector, which takes out the charges in theform of an electrical signal for reproduction of the sound. Otherfeatures can be derived as in the case of the video recording.

6. Summary The particularities of the invention described in the aboveare summarized as follows:

1. The invention relates to a recording device which comprises a mixtureof at least a semiconductor and an electrical insulator, a carriertransformer brought into contact with the mixture, another electricalinsulator brought into contact with the mixture on the opposite side ofthe carrier transformer, and an electrode either directly or indirectlybrought into contact with the another electrical insulator on theopposite side of the mixture.

2. The device according to the invention has a prominent effect that anelectric charge is storaged in the mixture of the semiconductor andinsulator, which charge has the same polarity with that of the carriertransformer with which the mixture is in contact.

3. An amount of charge stored in the mixture varies depending uponapplied voltage and a time of voltage application, and can be preservedeven in a light space.

4. When the semiconductor contained in the mixture is of P- type inwhich holes act as majority carriers, a remarkably greater amount ofcharge can be obtained than with a N-type semiconductor.

5. By the addition of a fluorescent body to the mixture, the amount ofcharge stored therein can be varied by application of light thereto.

6. By the addition of a ferroelectric substance to the mixture, theamount of charge stored in the mixture can be increased. 7. By theaddition of both of the fluorescent phosphor and the ferroelectricsubstance to the mixture, the increased amount of charge stored thereincan be varied by application of light thereto.

8. By the addition of a metal, which shows a photovoltaic effect incombination with the semiconductor included in the mixture, to themixture, the amount of charge stored therein can be increased byapplication of light thereto.

9. By bringing the mixture into contact with an insulator such aspolystyrene or polyethylene having little residual charge due toabsorption current, the amount of stored charge can be abruptly variedby application of light and AC voltage to the mixture.

10. By interposing a fluorescent layer between the insulator and theelectrode of transparent nature, the amount of charge stored in themixture can be varied by application of light thereto.

1 1. By interposing a photoconductor layer between the insulator and thetransparent electrode, the amount of charge stored in the mixture can bevaried by application of light thereto.

12. By adding a fluorescent phosphor to the mixture of the semiconductorand the insulator, latent images of positive and negative charges cansimultaneously be formed and thus it is possible to obtain a sensitivelayer suitable for electrophotography having a remarkably high resolvingpower and sensitivity.

13. The device of the invention, when applied to audio and videorecording, can provide a high degree of resolving power and fidelity.

From the foregoing detailed description, it will be understood that thepresent invention is based on a principle that a mixture of at least asemiconductor and an insulator is brought into contact with a carriertransformer, and electric charges are injected into the mixture from thecarrier transformer in contact with the mixture, the charges beingprevented from further movement by another insulator brought intocontact with the mixture and thus storaged in the mixture. Thisprinciple has not been known at all in the prior art, and therefore thedevice of the invention based on this principle is quite novel.

What is claimed is:

l. A recording device comprising a cohesive layer of a mixture ofsemiconductor particles dispersed in an electrical insulator, a firstelectrode contacting one side of said layer, a solid electricalinsulator having one side contacting the opposite side of said layer, atransparent second electrode disposed adjacent the opposite side of saidsolid electrical insulator, and a photoconductive layer interposedbetween and in physical contact with both said solid electricalinsulator and said transparent electrode, said cohesive andphotoconductive layers being coextensive with each other, the amount ofsaid semiconductor particles dispersed in said cohesive layer beingeffective upon application of a voltage between said electrodes toresult in a charge of the same polarity as said first electrode beingstored in said cohesive layer.

